This invention relates to a method for suppressing chatter vibrations, particularly self-excited chatter vibrations caused in a machine tool when in operation.
These are two different kinds of chatter vibration; one is called "forced chatter vibration" and the other "self-excited chatter vibration". Forced chatter vibration is caused for instance by a motor when working or by a train of gears when rotating and engaging with each other, and is transmitted from such vibration sources to the surface of a workpiece which is being machined. This sort of vibration is not caused by the cutting zone. In contrast to this, the self-excited chatter vibration is caused in the cutting zone. More specifically, for instance a bit used in cutting or peeling a workpiece is not stable. This is due to the uneven surface of the workpiece, intervenient fractures of metal swarf and other factors. The surface of the workpiece thus machined becomes sinusoidal. This sinusoidal wave on the surface of the workpiece causes the chatter vibration of the tool when machining the workpiece for the second time. Thus, on the surface of the workpiece there will subsequently appear a different sinusoidal pattern each time a single machining has been performed. The last sinusoidal pattern is different from the preceding one in phase by a certain amount. It has been found that the maximum energy to produce the self-excited chatter vibration is stored when there is a definite phase difference between each sinusoidal pattern and the one preceding it. In this connection the self-excited chatter vibration will be suppressed by changing the phase difference in successive sinusoidal patterns.
As a method for suppressing the self-excited chatter vibration it has been hitherto proposed that the rotation speed of the workpiece be changed during is machining so as to alter the phase pitch between successive patterns. This is effective in suppressing the self-excited vibration. If the rotation speed of the workpiece is changed in the course of machining, however the bending displacement of the tool and the machinability of the workpiece will accordingly vary with the result that the working accuracy is lowered.
The object of this invention is to provide a method for suppressing the self-excited chatter vibration without recourse to changing the rotation speed of either the workpiece or the tool in machining.